1.Field of the Invention
The present invention relates to a diagnostic X-ray apparatus which can obtain a fluorogram and a tomogram (CT image).
2. Description of the Related Art
Conventionally, simulation for a treatment program is performed in order to determine an amount of X-ray emission, a direction of X-ray emission, and the like prior to X-ray diagnosis and X-ray treatment. For the purpose of this simulation, a tomogram is often obtained in addition to a fluorogram. However, since a conventional X-ray fluoroscopic apparatus can obtain only a fluorogram, a tomogram must be obtained using another CT apparatus. This operation is complicated and timeconsuming. In addition, when a patient is exposed with X-rays twice, the health of the patient may be adversely affected. Therefore, a demand has arisen for developing an X-ray diagnostic apparatus which can obtain a tomogram in addition to a fluorogram.
FIG. 1 shows an arrangement of a diagnostic X-ray apparatus which is constructed by additionally providing a function for obtaining a tomogram on the basis of the conventional X-ray fluoroscopic apparatus. The X-ray apparatus in FIG. 1 has been developed in accordance with the above-mentioned demand. X-ray beam emitted from an X-ray tube 14 is emitted onto one slice of an object 10 to be examined on a bed 12 through a diaphragm 16 for defining the slice having a predetermined thickness. The diaphragm 16 has a rectangular aperture perpendicular to the axis of the object 10. The slice of the object 10 is exposed with fan X-ray emitted from the diaphragm 16. When a fluorogram is obtained, the diaphragm 16 is removed. A case wherein a tomogram is obtained will be described hereinafter. The X-ray transmitted through one slice of the object 10 is incident on an image intensifier 18. The transmitted X-ray representing the degree of X-ray absorbance of tissues in the slice is converted into a light beam, and is output. The light beam is incident on a TV camera 22 through an optical system 20, and is converted into an analog signal, thus obtaining a projection signal representing the degree of X-ray absorbance of tissues in the slice. The X-ray tube 14, the diaphragm 16, the image intensifier 18, the optical system 20, and the TV camera 22 are aligned along a line, and can be integrally rotated in a direction indicated by an arrow A in FIG. 1 with respect to the object 10 in order to obtain a tomogram. In addition, in order to obtain a fluorogram from an arbitrary direction, the above units can be arranged to face any direction with respect to the object 10.
The analog projection signal output from the TV camera 22 is converted into a digital signal by an A/D converter 24, thus obtaining X-ray projection data. While the X-ray tube 14 and the like are rotated once in the direction indicated by the arrow A in FIG. 1 around the object 10, an X-ray is emitted for each predetermined angle, and X-ray projection data at each angle is written in a memory 26. The projection data read out from the memory 26 is supplied to an image reconstruction processor 28, and a tomogram of the slice is reconstructed. The obtained tomogram is input to a display 32 through a D/A converter 30, and is displayed.
The X-ray apparatus with the above arrangement can acquire X-ray projection data in the same manner as in the conventional CT apparatus by emitting an X-ray onto one slice of the object through the diaphragm 16, and by using the image intensifier 18 and the TV camera 22 as X-ray detectors. When a fluorogram is obtained, the diaphragm 16 may be removed to emit X-ray onto a given area of the object, and an output from the TV camera 22 or the memory 26 may be displayed or recorded.
Such an X-ray apparatus, however, has the following problems. A screen of the image intensifier 18 has a circular shape and an imaging area of the TV camera 22 has a square shape in order to obtain a fluorogram. When a tomogram is obtained, however, an X-ray is emitted onto a slice of the object 10 through the diaphragm 16. Therefore, as shown in FIG. 2, a light beam from the image intensifier 18 is only incident on a strip region 34 of an imaging area 33 of the TV camera 22. The strip region 34 corresponds to the slice. For this reason, when the TV camera 22 normally performs a scanning operation, i.e., the entire imaging area 33 (regions 36, 34, and 38) is scanned, the regions 36 and 38 which receive no light beams are unnecessarily scanned. This operation is a waste of time. Therefore, when a tomogram is obtained, a time period required for acquiring projection data is unnecessarily prolonged. As a result, a time for obtaining a tomogram is undesirably prolonged. In addition, since unnecessary data read out from the regions 36 and 38 are written in the memory 26, the memory 26 cannot be effectively used.